In a standard Radio Frequency-Identification (RF-ID) system, an interrogating antenna, sometimes called the transmitter antenna, transmits a power burst signal of some predetermined duration to power up the passive transponder in the field to respond. Once the transponder is fully charged from the interrogation signal, the power burst signal is damped at the interrogator, and the transponder transmits it response telegram. The response telegram generally consists of identification information and/or sensor or other data and is received by the interrogator. If a response telegram is received, then the interrogator knows that the transponder lies within the read range of the interrogation antenna. However, generally, with standard RF-ID interrogation equipment, it is not possible to determine the exact physical position of a transponder within the read range of the antenna due to the many variables involved. Some other the relevant variables are the distance between the reader and antenna, interrogation antenna size, interrogation field strength, orientation of the transponder with respect to the antenna and ambient noise levels.
With enough transponders located across an area, the approximate location of a particular object associated with a particular transponder may be achieved, but this solution will also probably be cost-prohibitive.